BACKGROUND. Walking impairment is frequent, appears early in the disease course of MS patients (MSP), and is perceived as the most disabling symptom. When walking, patients get tired more and differently ... [more ▼]

BACKGROUND. Walking impairment is frequent, appears early in the disease course of MS patients (MSP), and is perceived as the most disabling symptom. When walking, patients get tired more and differently than healthy people (HP) [Phan-Ba et al PLOS 2012]. This limits their walking perimeter. Understanding this phenomenon is thus important to suggest adequate therapies at the right time. OBJECTIVE. Our aim is to understand how MSP get tired while walking compared to HP. Two groups of MSP are considered: those with a low disability level (MSPL) and those with a high one (MSPH). We consider two criteria to measure the disability: the EDSS and the deceleration index (DI) [Phan-Ba et al PLOS 2012]. The limit between the groups is set at DI=0.8 and EDSS=3 (inclusive for MSPL). METHODS. Many gait characteristics (GC) have been measured with the system GAIMS along a 500m path walked as fast as possible. The dataset gathers 464 visits of HP and 70 of MSP. Some people have been assessed several times. There are 33 visits in the group MSPL with the EDSS criterion, and 25 with the DI criterion. Statistical tests (Welch) were performed on the differences and relative differences of the GC measured during the first and last 100m of the test to detect differences between HP and MSPL, and between MSPL and MSPH, as in [ECTRIMS 2012 P755]. RESULTS. Both criteria for defining the groups lead to similar conclusions. For many GC, the distributions of the variations are significantly different between MSPL and MSPH. The largest difference is for the relative difference of speed (p=0.000119 for EDSS and p=0.000021 for DI). In contrast, only the variation of the average lateral distance between the feet, which is related to the size of the base of support (and thus to the balance) shows a very significant difference between HP and MSPL (p=0.000116 for EDSS and p=0.000120 for DI). The balance does not seem to change much from MSPL to MSPH. Besides, we note that the variance decreases slightly from HP to MSPL and increases a lot from MSPL to MSPH. CONCLUSIONS. Statistically, from the motor fatigue point of view, it seems that the course of the MS disease is divided in two different stages. In the first one, MSP get more tired than HP because of a deterioration of the balance. Then, in the second one, their fatigue becomes related to a faster decrease of the walking speed. This suggests that physical therapy exercises focused on the balance could be given to MSP in the early stage of the disease. [less ▲]

By construction, a video is a series of ordered frames, whose order is defined at the time of the acquisition process. Background subtraction methods then take this input video and produce a series of ... [more ▼]

By construction, a video is a series of ordered frames, whose order is defined at the time of the acquisition process. Background subtraction methods then take this input video and produce a series of segmentation maps expressed in terms of foreground objects and scene background. To our knowledge, this natural ordering of frames has never been questioned or challenged. In this paper, we propose to challenge, in a prospective view, the natural ordering of video frames in the context of background subtraction, and examine alternative time orderings. The idea consists to change the order before background subtraction is applied, by means of shuffling strategies, and to re-order the segmentation maps afterwards. For this purpose, we propose several shuffling strategies and show that, for some background subtraction methods, results are preserved or even improved. The practical advantage of time shuffling is that it can been applied to any existing background subtraction seamlessly. [less ▲]

in 16th International Society for Music Information Retrieval Conference (2015, October)

In this paper, we evaluate a set of methods for combining features for cover song identification. We first create multiple classifiers based on global tempo, duration, loudness, beats and chroma average ... [more ▼]

In this paper, we evaluate a set of methods for combining features for cover song identification. We first create multiple classifiers based on global tempo, duration, loudness, beats and chroma average features, training a random forest for each feature. Subsequently, we evaluate standard combination rules for merging these single classifiers into a composite classifier based on global features. We further obtain two higher level classifiers based on chroma features: one based on comparing histograms of quantized chroma features, and a second one based on computing cross-correlations between sequences of chroma features, to account for temporal information. For combining the latter chroma-based classifiers with the composite classifier based on global features, we use standard rank aggregation methods adapted from the information retrieval literature. We evaluate performance with the Second Hand Song dataset, where we quantify performance using multiple statistics. We observe that each combination rule outperforms single methods in terms of the total number of identified queries. Experiments with rank aggregation methods show an increase of up to 23.5 % of the number of identified queries, compared to single classifiers. [less ▲]

Fires in buildings are characterized by a heating phase followed by a cooling phase, yet the effects of the latter on structures are not well covered in the current approaches to structural fire ... [more ▼]

Fires in buildings are characterized by a heating phase followed by a cooling phase, yet the effects of the latter on structures are not well covered in the current approaches to structural fire engineering. Indeed the actual requirement of non-occurrence of structural failure at peak temperature does not guarantee against a delayed failure during or after the cooling phase of a fire, which puts at risk the fire brigades and people proceeding to a building inspection after a fire. Therefore there is an urgent need to better comprehend and characterize the materials and structures behavior under decreasing temperatures. Sensitivity to delayed failure of a structural component depends on its typology and constituting materials. In particular, two structural components with the same Fire Resistance rating (R) under standardized fire may exhibit very distinct behavior under natural fire, one of them being more prone to delayed failure than the other. With the aim of quantifying this effect, a new indicator is proposed that characterizes the performance of structures under natural fire conditions. The paper presents the methodology to derive this new indicator as well as results for different typologies of structural components. Parametric analyses highlight the prime influence of constitutive material and thermal inertia of the element on the post-peak behavior. Used in conjunction with the Fire Resistance rating, it is shown how the new indicator carries additional and significant information for classifying structural systems in terms of their fire performance and propensity to delayed failure. [less ▲]

This doctoral study characterizes, for simple geometries, the cardiac autonomous electrical activity induced by the mechanical deformations of the myocardium via the mechano-electric feedback within a ... [more ▼]

This doctoral study characterizes, for simple geometries, the cardiac autonomous electrical activity induced by the mechanical deformations of the myocardium via the mechano-electric feedback within a thermo-electro-mechanical framework. The underlying fundamental mechanisms are highlighted and discussed in detail. In a healthy heart, the mechano-electric feedback acts as a regulator able to damp mechanical perturbations undergone by the heart, by appropriately modulating electrical activity shortly after these perturbations. In this way, a new healthy electromechanical situation is recovered. However, under certain conditions, this feedback can be a generator of dramatic cardiac arrhythmias by inducing local electrical depolarizations resulting from abnormal cardiac muscle tissue deformations. These local perturbations can then propagate in the whole heart and, thus, lead to global cardiac dysfunctions. The one- and two-dimensional models developed in this work to study the arrhythmogenic consequences of the mechano-electric feedback within a thermo-electro-mechanical framework account for three couplings: the excitation-contraction coupling, the mechano-electric feedback, and the thermo-electric coupling. The excitation-contraction coupling allows the mechanical contraction of cardiac muscle cells resulting from the electrical excitation of these cells, triggered by a propagating action potential initially generated by the sino-atrial node in a healthy heart. The mechano-electric feedback takes into account the influence of mechanical deformations on the electrical activity, both at the cell and the macroscopic level. The thermo-electric coupling then modulates certain electrical properties due to a temperature change. The excitation-contraction coupling is modeled in a phenomenological way by combining the Aliev-Panfilov model and the Rogers-McCulloch model. The propagation of the electrical excitation through cardiac muscle tissue is modeled by using the monodomain approach. The mechano-electric feedback is taken into account by considering two different contributions, namely the physiological contribution (physiological feedback) and the geometric contribution (geometric feedback). The physiological feedback consists in the onset of stretch-activated currents due to the deformations of the cardiac muscle tissue via specific mechanosensitive channels. Regarding the geometric feedback, it simply reflects that the propagation of the depolarization waves is altered by the deformations of the geometry. The thermo-electric coupling is modeled via a dependence with respect to the temperature which is exponential for the gating kinetics of ion channels, exponential for the kinetics of the active tension development in cardiomyocytes, and linear for the ionic conductances. This study shows that the mechano-electric feedback can be arrhythmogenic under specific conditions. In particular, this work clearly reveals that the size of the domain and the importance of stretch-activated currents are key factors in the behavior of the autonomous electrical activity induced by the mechano-electric feedback. This doctoral study also shows that temperature variations such as those undergone by the heart during therapeutic hypothermia or hyperthermia play a central role in the cardiac electromechanical behavior. Moreover, this work emphasizes the influence of the initial conditions on the electromechanical behavior of cardiac tissue. In the one-dimensional framework, an important result of this work is that the disappearance of the autonomous electrical activity induced by the deformations of the cardiac muscle can be associated with different types of bifurcation phenomena, depending on the values of the parameters. These bifurcations, which correspond in fact to different ways for the AEA to vanish, are emphasized and discussed in detail. [less ▲]

Data recording with Phase Change Materials is a much studied topic as the writing/erasing characteristics, cyclability and downscaling properties of these materials allow for efficient data storage in ... [more ▼]

Data recording with Phase Change Materials is a much studied topic as the writing/erasing characteristics, cyclability and downscaling properties of these materials allow for efficient data storage in future generations of devices. Nevertheless, some aspects of phase change materials are limiting their performances and delaying their wider technological application. First, aging phenomena are common to all amorphous structures, but of special importance PCMs since it impedes the realization of multi-level memories. Different interpretations have been proposed, but we focus here on the structural relaxation of amorphous GeTe, chosen because it is the simplest system that is representative of the wider class of GST alloys, lying along the GeTe-Sb2Te3 composition line of the GeSbTe phase diagram. One difficulty encountered in the simulation of these amorphous systems is that the direct generation of an amorphous structure by quenching a liquid using Density Functional Theory (DFT) based Molecular Dynamics leads to one sample with a small number of atoms, and, hence of small number of atomic environments. Here we sample a large number of local atomic environments, corresponding to different bonding schemes, by chemically substituting different alloys, selected to favor different local atomic structures. This enables spanning a larger fraction of the configuration space relevant to aging. Our results support a model of the amorphous phase and its time evolution that involves an evolution of the local (chemical) order towards that of the crystal. On the other hand its electronic properties drift away from those of the crystal, driven by an increase of the Peierls-like distortion of the local environments in the amorphous, as compared to the crystal [1]. A second problem faced by PCMs is the fact that data recording is limited at high temperature due to the increased propensity to recrystallize. One approach to counter this is to stabilize the PCM using impurity atoms such as C or N. Using DFT and the analysis of the mechanical properties (constraints theory), we demonstrate how these impurity atoms modify the rigidity of the network, which is experimentally correlated with the activation energy for crystallization [2]. Finally, the crystal phase itself has been shown to have variable conductivities depending on the thermal history and annealing conditions. If this could be used profitably for multi-level recording, it also indicates that the crystal is undergoes some temporal evolution. Using DFT, we clarify the stability behavior of GST crystal and show that the metal-insulator transition is driven by the migration of intrinsic vacancies and an Anderson localization transition [3]. [1] J.Y Raty, W. Zhang, J. Luckas, C. Chen, R. Mazzarello, C. Bichara and M. Wuttig, Nat. Comm. (2015) [2] G. Ghezzi, J.Y. Raty, S. Maitrejean, A. Roule, E. Elkaim and F. Hippert, Applied Physics Letters, 99 (2011) 151906 [3] W. Zhang, A. Thiess, P. Zalden, R. Zeller, P. H. Dederichs, J-Y. Raty, M.Wuttig, S. Blügel et R. Mazzarello, Nature Materials 11 (2012) 952 [less ▲]

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets ... [more ▼]

We present an algorithm based on an Ant Colony System to deal with a broad range of Dynamic Capacitated Vehicle Routing Problems with Time Windows, (partial) Split Delivery and Heterogeneous fleets (DVRPTWSD). Besides the traditional distance criterion, we address the important case of responsiveness. Responsiveness is defined here as completing a delivery as soon as possible, within the time window, such that the client or the truck may restart its activities. This is crucial for many production or service activities in different fields: express parcel deliveries, taxi services, Just in Time production, express repair services, medical care, petrol station replenishment, etc. We develop an interactive web-based solution to allow dispatchers to take new information into account in real-time. The algorithm and its parametrization were tested on real and artificial instances. We first illustrate our approach with a problem submitted by Liege Airport, the 8th biggest cargo airport in Europe. The goal is to develop a decision system to optimize the journey of the refueling trucks. We then consider some classical VRP benchmarks with extensions for more complex problems. [less ▲]

In his Critic of pure reason, Immanuel Kant notoriously claimed that, being grounded on the forms of sense intuition, arithmetical and geometrical propositions are both synthetic (i.e. informative) and a ... [more ▼]

In his Critic of pure reason, Immanuel Kant notoriously claimed that, being grounded on the forms of sense intuition, arithmetical and geometrical propositions are both synthetic (i.e. informative) and a priori. Bernard Bolzano, followed in this by the logicist movement (from Gottlob Frege to Rudolf Carnap), answered that the generality and necessity of mathematical propositions and proofs can only be grounded on conceptual analysis. Even though, just like Frege, he is one of the fathers of formal logic, Charles Sanders Peirce provides some semiotic reasons to think that Kant was right: diagrams do convey general meanings and provide some knowledge which is necessary yet non-trivial. Unlike logical analysis, visual presentation of concepts in schemas or diagrams helps to explore concepts by stressing some of their “side” features in such a way that new knowledge is gained: « diagrams evolve what was involved » (CP4/86). This is why, according to Kant’s notion of intuitive construction, mathematical inferences are not merely deductive but are inventive and ampliative. My talk aims at identifying some iconic virtues of diagrams which, according to Peirce, explain their epistemic productivity. A first one lies in the “formal” nature of icons, which allows them to express syntactic relations between descriptive (symbols) and demonstrative (indices) components of structured information. On this respect, even algebraic and ideographic expressions are icons exhibiting a general form – a “rheme” – in which places for indices are filled with variables “x” and “y” meaning “any individual”. For this reason, even though they are singular, diagrams are “abstractions” in the sense that they represent relations rather than their terms. Only with this in prospect can a second, and more studied, feature of diagrams matter, namely their two-dimensionality, which helps to exhibit complex relations that cannot be seen on linear linguistic expressions. Finally, a third feature of diagrams lies in their imaginary rather than referential character. Icons connote without denoting, and therefore they can be informational without this information being limited to singular individuals. Furthermore, this non referential character of icons is what makes them open to virtual exploratory manipulations that allow to consider and investigate possibilities which in turn inform us on not obvious properties of the presently visible configuration. [less ▲]

The aim of this work is to develop a stochastic multiscale model for polycrystalline materials, which accounts for the uncertainties in the micro-structure. At the finest scale, we model the micro ... [more ▼]

The aim of this work is to develop a stochastic multiscale model for polycrystalline materials, which accounts for the uncertainties in the micro-structure. At the finest scale, we model the micro-structure using a random Voronoi tessellation, each grain being assigned a random orientation. Then, we apply a computational homogenization procedure on statistical volume elements to obtain a stochastic characterization of the elasticity tensor at the meso-scale. A random field of the meso-scale elasticity tensor can then be generated based on the information obtained from the SVE simulations. Finally, using a stochastic finite element method, these meso-scale uncertainties are propagated to the coarser scale. As an illustration we study the resonance frequencies of MEMS micro-beams made of poly-silicon materials, and we show that the stochastic multiscale approach predicts results in agreement with a Monte Carlo analysis applied directly on the fine finite-element model, i.e. with an explicit discretization of the grains. [less ▲]